Critical dimensions (CD) of semiconductor devices continue to shrink. With smaller CD comes increased attention to minimizing errors associated with the photolithography processes used to make the devices. Common photolithography errors that are monitored include those from wafer and mask misalignment. Indeed, misalignment of the mask with respect to the wafer causes an element of a device to be formed at an improper position. If the alignment is off by an unacceptable amount, the devices do not function properly.
Another error of photolithography to be monitored is the error associated with photolithographic shot placement. During device processing a single mask may be used multiple times to expose the semiconductor wafer. This is often the case when the pattern of the mask is placed and shot (i.e., exposed) multiple times across the same device or across multiple devices on the same wafer. Improper alignment of the shot placement, however, causes a device or an element of a device to be formed at an improper position. Again, if the alignment is off by an unacceptable amount, an individual device or all of the devices, on a wafer do not function properly.
Unfortunately, however, the methods and devices commonly used to inspect for errors are complicated and are limited to inspecting only a few types of errors that can arise during manufacturing. Accordingly, embodiments of the invention described herein improve the error inspection processes and can inspect semiconductor wafers for additional types of errors that are currently neglected during manufacturing.